Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L9/00—Compositions of homopolymers or copolymers of conjugated diene hydrocarbons
  • C08L9/06—Copolymers with styrene
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
  • B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
  • B60C1/00—Tyres characterised by the chemical composition or the physical arrangement or mixture of the composition
  • B60C1/0016—Compositions of the tread
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/02—Elements
  • C08K3/04—Carbon
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/34—Silicon-containing compounds
  • C08K3/36—Silica
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L7/00—Compositions of natural rubber
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
  • C08K3/20—Oxides; Hydroxides
  • C08K3/22—Oxides; Hydroxides of metals
  • C08K2003/2296—Oxides; Hydroxides of metals of zinc
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K2201/00—Specific properties of additives
  • C08K2201/002—Physical properties
  • C08K2201/006—Additives being defined by their surface area
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2205/00—Polymer mixtures characterised by other features
  • C08L2205/03—Polymer mixtures characterised by other features containing three or more polymers in a blend
  • C08L2205/035—Polymer mixtures characterised by other features containing three or more polymers in a blend containing four or more polymers in a blend
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T10/00—Road transport of goods or passengers
  • Y02T10/80—Technologies aiming to reduce greenhouse gasses emissions common to all road transportation technologies
  • Y02T10/86—Optimisation of rolling resistance, e.g. weight reduction 

Definitions

• the present invention relates to a rubber composition for a tread and a tire having a tread composed of the rubber composition.
• a natural rubber and a styrene-butadiene rubber having excellent chipping resistance are used as a rubber component for a tread rubber and reinforcing agents such as carbon black and silica having high reinforceability are compounded.
• abrasion resistance is also demanded as durability of a tire, and in the case of all-season tires used mainly on a smooth road, enhancement of abrasion resistance is aimed by compounding a butadiene rubber.
• a butadiene rubber is compounded in a rubber for a tread, there is a tendency of enhancing abrasion resistance, but chipping resistance is worsened, and thus, there is a problem that compatibility of the both characteristics is difficult.
• JP 2014-024890 A describes a rubber composition for a tread, in which abrasion resistance and block crack resistance are improved by allowing the rubber composition to comprise crystallized carbon black.
• abrasion resistance and block crack resistance are improved by allowing the rubber composition to comprise crystallized carbon black.
• compatibility there is a room for improvement in compatibility between the both characteristics.
• An object of the present invention is to provide a rubber composition for a tread having a good abrasion resistance, particularly abrasion resistance for running on a rough road surface (unpaved rough road surface) and a tire having a tread composed of the rubber composition.
• a rubber composition for a tread comprising predetermined amounts of an isoprene rubber, a butadiene rubber and a styrene-butadiene rubber and carbon black having a predetermined nitrogen adsorption specific surface area has a good abrasion resistance. Further, the inventor has found that in a preferred embodiment, chipping resistance of a rubber composition for a tread is enhanced, and has completed the present invention.
• the present invention relates to:
• a rubber composition for a tread comprising 10 to 70 parts by mass of carbon black having a nitrogen adsorption specific surface area of 130 m 2 /g or more based on 100 parts by mass of a rubber component comprising 50 to 70% by mass of an isoprene rubber, 10 to 30% by mass of a butadiene rubber and 20 to 40% by mass of a styrene-butadiene rubber, [2] the rubber composition for a tread of the above [1], having 70° CE* of 6.2 or more, [3] the rubber composition for a tread of the above [1] or [2], having 70° C tan ⁇ of 0.13 or less, [4] the rubber composition for a tread of any of the above [1] to [3], wherein a silica content is not less than 0 part by mass and not more than 10 parts by mass, [5] the rubber composition for a tread of any of the above [1] to [4], wherein a styrene content of the styrene
• the rubber composition comprises a styrene-butadiene rubber (SBR), and thereby fine particle carbon which is difficult to disperse in a butadiene rubber (BR) is dispersed satisfactorily, a reinforcing effect by carbon black is exhibited and abrasion resistance when running on a rough road is enhanced.
• SBR styrene-butadiene rubber
• compatibility between the SBR and the BR is enhanced and carbon black existing in an SBR phase is also distributed to a BR phase. Therefore, a rubber strength of the BR phase is increased, and abrasion resistance when running on a rough road is enhanced.
• the tire having a tread composed of the rubber composition of the present invention is good in abrasion resistance, particularly abrasion resistance for running on a rough road.
• the rubber composition for a tread of one embodiment of the present invention is characterized by comprising an isoprene rubber, a butadiene rubber (BR), a styrene-butadiene rubber (SBR) and carbon black having a predetermined nitrogen adsorption specific surface area.
• the rubber composition is a rubber composition for a tread comprising 10 to 70 parts by mass of carbon black having a nitrogen adsorption specific surface area of 130 m 2 /g or more based on 100 parts by mass of a rubber component comprising 50 to 70% by mass of an isoprene rubber, 10 to 30% by mass of a butadiene rubber and 20 to 40% by mass of a styrene-butadiene rubber.
• a numerical range is shown using “to”, it includes numerical values at both sides thereof.
• the rubber composition for a tread of one embodiment of the present invention by dispersing a styrene butadiene rubber (SBR) in an isoprene/butadiene polymer, an impact generated when running on a rough road is relaxed.
• SBR styrene butadiene rubber
• the rubber composition comprises a predetermined amount of small particle size carbon black having a nitrogen adsorption specific surface area of 130 m 2 /g or more, the small particle size carbon black is dispersed in the neighborhood of a boundary of each phase of the isoprene rubber, the BR and the SBR, and a contact area of the SBR with carbon black increases.
• bonding between the respective phases of the isoprene rubber, the BR and the SBR is made strong, thereby making it possible to obtain a rubber composition being capable of effectively absorbing an impact generated when running on a rough road. Further, it can be considered that by use of the small particle size carbon black, a reinforcing effect on the rubber composition is enhanced and abrasion resistance and chipping resistance are enhanced
• Examples of a rubber component suitably used in one embodiment of the present invention include a styrene butadiene rubber (SBR), an isoprene rubber and a butadiene rubber (BR).
• SBR styrene butadiene rubber
• BR butadiene rubber
• Examples of the usable isoprene rubber include those usually used in a tire industry, for example, an isoprene rubber (IR), a natural rubber and the like.
• Examples of the natural rubber include modified natural rubbers such as an epoxidized natural rubber (ENR), a hydrogenated natural rubber (HNR), a deproteinized natural rubber (DPNR), an ultra pure natural rubber (UPNR) and a grafted natural rubber besides an un-modified natural rubber (NR). These rubbers may be used alone, or may be used in combination of two or more thereof.
• NR is not limited particularly, and those which are commonly used in a tire industry can be used. For example, there are SIR20, RSS#3, TSR20 and the like.
• a content of the isoprene rubber in the rubber component is not less than 50% by mass, preferably not less than 52% by mass, more preferably not less than 55% by mass. When the content is less than 50% by mass, there is a tendency that an effect of the present invention becomes insufficient.
• the content of the isoprene rubber is not more than 70% by mass, preferably not more than 68% by mass, more preferably not more than 65% by mass. When the content exceeds 70% by mass, crack growth resistance tends to decrease.
• BR is not limited particularly, and examples of usable BRs include BRs usually used in a tire industry, for example, a BR having a content of cis-1,4 bond of less than 50% (low cis BR), a BR having a content of cis-1,4 bond of not less than 90% (high cis BR), a rare-earth butadiene rubber (rare-earth BR) synthesized using a rare-earth element catalyst, a BR comprising syndiotactic polybutadiene crystals (SPB-containing BR), a modified BR (high cis modified BR, low cis modified BR) and the like.
• a high cis BR is preferable for the reason that abrasion resistance is good.
• Examples of the high-cis BRs include BR1220 available from ZEON CORPORATION, BR130B, BR150B and BR150L available from Ube Industries, Ltd., BR730 available from JSR Corporation and the like.
• the rubber component comprises a high cis BR
• low temperature characteristics and abrasion resistance can be enhanced.
• Examples of the rare-earth BRs include BUNA-CB25 manufactured by Lanxess K.K. and the like.
• SPB-containing BR is not one in which 1,2-syndiotactic polybutadiene crystals are simply dispersed in the BR, but one in which 1,2-syndiotactic polybutadiene crystals are chemically bonded with the BR and dispersed therein.
• SPB-containing BR examples include VCR-303, VCR-412 and VCR-617 manufactured by Ube Industries, Ltd. and the like.
• Examples of a modified BR include a modified BR (tin modified BR) obtained by performing polymerization of 1,3-butadiene with a lithium initiator and then adding a tin compound, and further having the molecular terminals bonded with a tin-carbon bond, a butadiene rubber (modified BR for silica) having an alkoxysilane condensate compound in an active terminal thereof and the like.
• modified BRs include BR1250H (tin-modified) manufactured by ZEON CORPORATION, S-modified polymer (modified for silica) manufactured by Sumitomo Chemical Industry Company Limited and the like.
• a content of the BR in the rubber component is not less than 10% by mass, preferably not less than 12% by mass, more preferably not less than 14% by mass. When the content is less than 10% by mass, there is a tendency that an effect of the present invention becomes insufficient.
• the content of the BR is not more than 30% by mass, preferably not more than 25% by mass, more preferably not more than 18% by mass. When the content exceeds 30% by mass, there is a tendency that chipping resistance is decreased and block cracks is easily generated.
• the cis 1,4-bond content (cis content) in the BR is preferably 90% or more, more preferably 93% or more, still more preferably 95% or more, from the viewpoint of durability and abrasion resistance. It can be considered that since in the case of a larger cis content, a polymer chain is arranged regularly, an interaction between the polymers becomes strong, a rubber strength is enhanced and abrasion resistance when running on a rough road is increased.
• a weight-average molecular weight (Mw) of the BR is preferably not less than 400,000, more preferably not less than 450,000, further preferably not less than 500,000 from the viewpoint of abrasion resistance and grip performance.
• the weight-average molecular weight is preferably not more than 2,000,000, more preferably not more than 1,000,000 from the viewpoint of crosslinking uniformity.
• the weight-average molecular weight of the BR can be calibrated with standard polystyrene based on measurement values determined with gel permeation chromatography (GPC) (GPC-8000 series manufactured by Tosoh Corporation; detector: differential refractometer; column: TSKGEL SUPERMALTPORE HZ-M manufactured by Tosoh Corporation).
• the SBR is not particularly limited.
• the SBR include a solution-polymerized SBR (S-SBR), an emulsion-polymerized SBR (E-SBR), a modified SBR thereof (modified S-SBR, modified E-SBR) and the like.
• the modified SBR include an end-modified and/or main-chain-modified SBR, a modified SBR coupled with a tin or silicon compound or the like (such as a condensate, one having a branch structure, etc.) and the like. Among these, S-SBR is preferable.
• S-SBR usable in one embodiment of the present invention examples include S-SBRs manufactured by JSR Corporation, Sumitomo Chemical Company, Limited, Ube Industries, Ltd., Asahi Kasei Corporation, ZEON CORPORATION, etc.
• a styrene content of the SBR is preferably not less than 5% by mass, more preferably not less than 7% by mass, further preferably not less than 10% by mass, for the reason that an effect of the present invention can be obtained sufficiently. Further, the styrene content is preferably not more than 15% by mass, more preferably not more than 13% by mass. When the styrene content exceeds 15% by mass, there is a tendency that heat generation is increased. It is noted that the styrene content of the SBR as used herein is calculated in accordance with 1 H-NMR measurement.
• a vinyl content of the SBR is preferably not less than 30 mol %, more preferably not less than 33 mol %, further preferably not less than 35 mol %.
• the vinyl content of the SBR is preferably not more than 45 mol %, more preferably not more than 42 mol %, further preferably not more than 40 mol %.
• the vinyl content of the SBR as used herein means an amount of 1,2-bond butadiene unit in the SBR, and is determined by an infrared absorption spectrum analysis method.
• a weight-average molecular weight (Mw) of the SBR is preferably not less than 200,000, more preferably not less than 300,000, further preferably not less than 400,000, particularly preferably not less than 500,000 from the viewpoint of abrasion resistance and grip performance.
• the Mw is preferably not more than 2,000,000, more preferably not more than 1,000,000 from the viewpoint of crosslinking uniformity. It is noted that the Mw can be calibrated with standard polystyrene based on measurement values determined with gel permeation chromatography (GPC) (GPC-8000 series manufactured by Tosoh Corporation; detector: differential refractometer; column: TSKGEL SUPERMALTPORE HZ-M manufactured by Tosoh Corporation).
• GPC gel permeation chromatography
• a content of the SBR in the rubber component is not less than 20% by mass, preferably not less than 22% by mass, more preferably not less than 25% by mass. When the content of the SBR is less than 20% by mass, there is a tendency that an effect of the present invention becomes insufficient.
• the SBR content is not more than 40% by mass, preferably not more than 37% by mass, more preferably not more than 35% by mass. When the SBR content exceeds 40% by mass, there is a tendency that heat generation is increased.
• rubber components other than the SBR, isoprene rubber and BR can be used.
• Crosslinkable rubber components usually used in a rubber industry can be used as the other rubber components. Examples thereof include a styrene-isoprene-butadiene copolymer (SIBR), a styrene-isobutylene-styrene block copolymer (SIBS), a chloroprene rubber (CR), an acrylonitrile-butadiene rubber (NBR), a hydrogenated nitrile rubber (HNBR), a butyl rubber (IIR), an ethylene propylene rubber, a polynorbornene rubber, a silicone rubber, a polyethylene chloride rubber, a fluorine-containing rubber (FKM), an acrylic rubber (ACM), a hydrin rubber and the like.
• SIBR styrene-isoprene-butadiene copolymer
• SIBS styrene-iso
• a complex elastic modulus (70° CE*) at 70° C. of the rubber composition for a tread under the conditions of an initial strain of 10%, a dynamic strain of 2% and a frequency of 10 Hz is preferably 6.2 MPa or more, more preferably 7.0 MPa or more, further preferably 7.5 MPa or more, particularly preferably 8.0 MPa or more from the viewpoint of abrasion resistance and chipping resistance.
• a tan ⁇ (70° C tan ⁇ ) at 70° C. of the rubber composition for a tread under the conditions of an initial strain of 10%, a dynamic strain of 2% and a frequency of 10 Hz is preferably 0.13 or lower, more preferably 0.11 or lower, further preferably 0.09 or lower.
• abrasion resistance tends to deteriorate by softening of a tread due to heat generation.
• the rubber composition for a tread according to one embodiment of the present invention is characterized by comprising a predetermined amount of small particle size carbon black having a nitrogen adsorption specific surface area of 130 m 2 /g or more.
• a nitrogen adsorption specific surface area (N 2 SA) of the small particle size carbon black is 130 m 2 /g or more, preferably 135 m 2 /g or more, more preferably 140 m 2 /g or more.
• N 2 SA nitrogen adsorption specific surface area
• an upper limit of the nitrogen adsorption specific surface area is not limited particularly, and is preferably 180 m 2 /g or less, more preferably 160 m 2 /g or less, further preferably 150 m 2 /g or less from the viewpoint of processability.
• the nitrogen adsorption specific surface area can be measured according to JIS K 6217-2 “Carbon black for rubber industry—Fundamental characteristics—Part 2: Determination of specific surface area—Nitrogen adsorption methods—Single-point procedures”.
• a content of the small particle size carbon black is not less than 10 parts by mass, preferably not less than 20 parts by mass, more preferably not less than 30 parts by mass, further preferably not less than 35 parts by mass based on 100 parts by mass of the rubber component.
• the content of the small particle size carbon black is not more than 70 parts by mass, preferably not more than 65 parts by mass, more preferably not more than 60 parts by mass.
• the content exceeds 70 parts by mass there is a tendency that heat generation is liable to arise.
• the rubber composition for a tread according to one embodiment of the present invention does not comprise carbon black having a nitrogen adsorption specific surface area (N 2 SA) of less than 130 m 2 /g.
• N 2 SA nitrogen adsorption specific surface area
• the content thereof is preferably not more than 30 parts by mass, more preferably not more than 20 parts by mass, further preferably not more than 10 parts by mass based on 100 parts by mass of the rubber component from the viewpoint of reinforceability.
• fillers other than the above-mentioned carbon black (other fillers), zinc oxide, stearic acid, antioxidants, processing aids, waxes, softening agents, vulcanizing agents, vulcanization accelerators and the like can be optionally compounded in the rubber composition for a tread in one embodiment of the present invention.
• fillers are not limited particularly, and examples thereof include silica, aluminum hydroxide, alumina (aluminum oxide), calcium carbonate, talc and the like. These fillers can be used alone or can be used in combination with two or more kinds thereof.
• Silica is not limited particularly, and examples thereof include silica prepared by a dry method (anhydrous silica), silica prepared by a wet method (hydrous silica) and the like. Hydrous silica prepared by a wet method is preferred for the reason that many silanol groups are contained.
• a nitrogen adsorption specific surface area (N 2 SA) of silica is preferably 80 m 2 /g or more, more preferably 100 m 2 /g or more from the viewpoint of durability and elongation at break.
• the nitrogen adsorption specific surface area of silica is preferably 250 m 2 /g or less, more preferably 220 m 2 /g or less from the viewpoint of fuel efficiency and processability. It is noted that herein the nitrogen adsorption specific surface area of silica is a value measured in accordance with ASTM D3037-93.
• the content thereof is preferably not less than 1 part by mass, more preferably not less than 3 parts by mass based on 100 parts by mass of the rubber component from the viewpoint of durability and elongation at break. Further, from the viewpoint of abrasion resistance, the content of silica is preferably not more than 10 parts by mass, more preferably not more than 8 parts by mass, further preferably not more than 6 parts by mass based on 100 parts by mass of the rubber component. It is noted that the content of silica may be 0 part by mass.
• Silica is preferably used in combination with a silane coupling agent.
• the silane coupling agent may be any silane coupling agents conventionally used in conjunction with silica in the rubber industry.
• the silane coupling agent include sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl) disulfide and bis(3-triethoxysilylpropyl) tetrasulfide; mercapto-based silane coupling agents such as 3-mercaptopropyltrimethoxysilane and NXT-Z100, NXT-Z45, NXT and the like manufactured and sold by Momentive Performance Materials (silane coupling agents having a mercapto group); vinyl-based silane coupling agents such as vinyltriethoxysilane; amino-based silane coupling agents such as 3-aminopropyltriethoxysilane; glycidoxy-based silane coupling agents such as ⁇ -glycidoxypropyl
• the content thereof is preferably 1 part by mass or more, more preferably 3 parts by mass or more based on 100 parts by mass of silica for the reason that sufficient effects of improving dispersibility of fillers and decreasing a viscosity can be obtained.
• the content of the silane coupling agent is preferably 12 parts by mass or less, more preferably 10 parts by mass or less based on 100 parts by mass of silica.
• the antioxidant is not particularly limited, and any antioxidants conventionally used in a field of rubbers can be used.
• examples of the antioxidant include quinoline-based antioxidants, quinone-based antioxidants, phenol-based antioxidants, phenylenediamine-based antioxidants and the like.
• the content thereof is preferably 0.5 part by mass or more, more preferably 0.8 part by mass or more based on 100 parts by mass of the rubber component.
• the content of the antioxidant is preferably 2.0 parts by mass or less, more preferably 1.5 parts by mass or less, further preferably 1.2 parts by mass or less based on 100 parts by mass of the rubber component from the viewpoint of dispersibility of the filler and the like, elongation at break and kneading efficiency.
• processing aid examples include fatty acid metal salts such as zinc stearate and the like.
• fatty acid soap processing aids such as Struktol EF44 and WB16 available from Schill & Seilacher Struktol GmbH.
• a compounding amount of the processing aid is preferably not less than 0.1 part by mass based on 100 parts by mass of a total amount of rubber components, and is preferably not more than 5 parts by mass, particularly preferably not more than 3 parts by mass.
• the content thereof is preferably not less than 0.5 part by mass, more preferably not less than 1 part by mass based on 100 parts by mass of the rubber component from the viewpoint of securing weather resistance of a rubber.
• the content thereof is preferably not more than 10 parts by mass, more preferably not more than 5 parts by mass, from the viewpoint of preventing whitening of a tire due to blooming of the wax on the surface of a tire.
• the content thereof is preferably not less than 0.2 part by mass, more preferably not less than 1 part by mass based on 100 parts by mass of the rubber component from the viewpoint of obtaining a vulcanization rate
• the content thereof is preferably not more than 10 parts by mass, more preferably not more than 5 parts by mass, from the viewpoint of processability.
• the content thereof is preferably not less than 0.5 part by mass, more preferably not less than 1 part by mass based on 100 parts by mass of the rubber component from the viewpoint of obtaining a vulcanization rate.
• the content thereof is preferably not more than 10 parts by mass, more preferably not more than 5 parts by mass, from the viewpoint of abrasion resistance.
• the softening agent means a component soluble in acetone, and examples thereof include oil such as process oil and vegetable fats and oils, liquid diene polymers and the like. These softening agents may be used alone or may be used in combination of two or more thereof. Among these, oil is preferred.
• oils examples include a process oil, vegetable fats and oils, or a mixture thereof.
• process oil examples include a paraffin process oil, a naphthenic process oil, an aromatic process oil (aromatic oil) and the like.
• vegetable oils and fats include castor oil, cotton seed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, tsubaki oil, jojoba oil, macadamia nut oil, tung oil, and the like.
• aromatic oil is preferred.
• the liquid diene polymer is not limited particularly as long as it is a liquid diene polymer having a weight-average molecular weight of not more than 50,000.
• examples thereof include a styrene-butadiene copolymer (rubber), a butadiene polymer (rubber), an isoprene polymer (rubber), an acrylonitrile-butadiene copolymer (rubber) and the like.
• liquid styrene-butadiene copolymer liquid styrene-butadiene rubber (liquid SBR)
• liquid SBR liquid styrene-butadiene rubber
• liquid BR liquid butadiene rubber
• the liquid butadiene polymer liquid butadiene rubber (liquid BR)
• an effect of enhancing abrasion resistance is remarkable.
• a weight-average molecular weight (Mw) of the liquid diene polymer is preferably not less than 1,000, more preferably not less than 1,500 for the reason that an effect of enhancing abrasion resistance is satisfactory.
• the weight-average molecular weight is preferably not more than 50,000, more preferably not more than 20,000, more preferably not more than 15,000 from the viewpoint of on-ice performance.
• weight-average molecular weight can be calibrated with standard polystyrene based on measurement values determined with gel permeation chromatography (GPC) (GPC-8000 series manufactured by Tosoh Corporation; detector: differential refractometer; column: TSKGEL SUPERMALTPORE HZ-M manufactured by Tosoh Corporation).
• GPC gel permeation chromatography
• a content of the softening agent is preferably not less than 1 part by mass, more preferably not less than 3 parts by mass based on 100 parts by mass of the rubber component from the viewpoint of processability.
• the content of the softening agent is preferably not more than 10 parts by mass, more preferably not more than 5 parts by mass from the viewpoint of block crack resistance and abrasion resistance.
• Sulfur is suitably used as the vulcanizing agent.
• usable sulfur include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur and the like.
• the content thereof is preferably 0.5 part by mass or more, more preferably 1.0 part by mass or more based on 100 parts by mass of the rubber component from the viewpoint of securing sufficient vulcanization reaction and obtaining a good grip performance and abrasion resistance.
• the content thereof is preferably 3.0 parts by mass or less, more preferably 2.5 parts by mass or less based on 100 parts by mass of the rubber component from the viewpoint of degradation.
• vulcanizing agents other than sulfur examples include a vulcanizing agent containing a sulfur atom such as TACKIROL V200 manufactured by Taoka Chemical Co., Ltd., DURALINK HTS (1,6-hexamethylene-sodium dithiosulfate dehydrate) manufactured by Flexsys, KA9188 (1,6-bis(N,N′-dibenzylthiocarbamoyldithio)hexane) manufactured by LANXESS K.K. and the like, an organic peroxide such as a dicumyl peroxide and the like.
• TACKIROL V200 manufactured by Taoka Chemical Co., Ltd.
• DURALINK HTS (1,6-hexamethylene-sodium dithiosulfate dehydrate) manufactured by Flexsys
• KA9188 1,6-bis(N,N′-dibenzylthiocarbamoyldithio)hexane
• an organic peroxide such as
• a vulcanization accelerator examples include sulfenamide-, thiazole-, thiuram-, thiourea-, guanidine-, dithiocarbamate-, aldehyde amine- or aldehyde ammonia-, imidazoline- and xanthate-based vulcanization accelerators. These vulcanization accelerators may be used alone or may be used in combination of two or more thereof. Among these, sulfenamide-based vulcanization accelerators, thiazole-based vulcanization accelerators and guanidine-based vulcanization accelerators are preferred, and sulfenamide-based vulcanization accelerators are preferred more.
• sulfenamide-based vulcanization accelerators include N-t-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N,N′-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS) and the like.
• TBBS N-t-butyl-2-benzothiazolylsulfenamide
• CBS N-cyclohexyl-2-benzothiazolylsulfenamide
• CBS N-cyclohexyl-2-benzothiazolylsulfenamide
• Examples of the thiazole-based vulcanization accelerator include 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide and the like. Among these, 2-mercaptobenzothiazole is preferable.
• Examples of the guanidine-based vulcanization accelerator include 1,3-diphenylguanidine, 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salt of dicatechol borate, 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, 1,3-di-o-cumenyl-2-propionylguanidine and the like.
• 1,3-diphenylguanidine is preferable.
• the content thereof is preferably not less than 0.5 part by mass, more preferably not less than 1.0 part by mass based on 100 parts by mass of the rubber component from the viewpoint of securing sufficient vulcanization rate.
• the content of the vulcanization accelerator is preferably not more than 10 parts by mass, more preferably not more than 5 parts by mass from the viewpoint of inhibiting blooming.
• the rubber composition for a tread according to one embodiment of the present invention can be prepared by a usual method.
• the rubber composition can be prepared, for example, by a method of kneading the above-mentioned components other than the vulcanizing agent and the vulcanization accelerator with a generally well-known kneading machine used in a rubber industry such as a Banbury mixer, a kneader or an open roll and then adding the vulcanizing agent and the vulcanization accelerator, followed by further kneading and then conducting vulcanization, or by other method.
• a generally well-known kneading machine used in a rubber industry such as a Banbury mixer, a kneader or an open roll
• a tire according to one embodiment of the present invention can be produced by a usual method using the above-mentioned rubber composition for a tread.
• the tire can be produced by subjecting an unvulcanized rubber composition obtained by kneading the above-mentioned components, to extrusion processing to a shape of a tire member such as a tread, and then laminating together with other tire members on a tire building machine and forming by a usual forming method, thus forming an unvulcanized tire, and heating and compressing this unvulcanized tire in a vulcanizer.
• a category of the tire according to one embodiment of the present invention is not limited particularly, and tires for a passenger car, heavy load tires for trucks, buses and the like, tires for two-wheel vehicles, run flat tires, pneumatic tires, etc. are preferable, and the tire according to one embodiment of the present invention is particularly suitably used as tires for steering of trucks. Further, the tire according to one embodiment of the present invention is good in abrasion resistance and chipping resistance, and therefore, is suitable for running on a rough road surface (unpaved rough road surface).
• BR UBEPOL BR150B (Mw: 440,000, high-cis BR, cis-1,4 bond content: 96%) manufactured by Ube Industries, Ltd.
• Carbon black 1 N134 (N 2 SA: 143 m 2 /g) manufactured by Tokai Carbon Co., Ltd.
• Carbon black 2 SHOBLACK N220 (N 2 SA: 114 m 2 /g) manufactured by Cabot Japan K. K.
• Antioxidant 1 NOCRAC 6C (N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine, 6PPD) manufactured by OUCHI SHINKO CHEMICAL INDUSTRIAL CO., LTD.
• Antioxidant 2 NOCRAC RD (poly(2,2,4-trimethyl-1,2-dihydroquinoline)) manufactured by OUCHI SHINKO CHEMICAL INDUSTRIAL CO., LTD.
• Stearic acid Stearic acid beads “Tsubaki” manufactured by NOF Corporation
• Zinc oxide Zinc Oxide No. 2 manufactured by Mitsui Mining & Smelting Co., Ltd.
• Sulfur Powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd.
• Vulcanization accelerator Nocceler NS (N-tert-butyl-2-benzothiazolylsulfeneamide (TBBS)) manufactured by OUCHI SHINKO CHEMICAL INDUSTRIAL CO., LTD.
• the obtained unvulcanized rubber composition was extruded and molded into the shape of a tire tread by an extruder equipped with a base having a predetermined shape, and then laminated with other tire members to form an unvulcanized tire, which was then press-vulcanized to manufacture a test tire (12R22.5, a tire for a truck and a bus).
• a complex elastic modulus (70° CE*) and tan ⁇ (70° C tan ⁇ ) at 70° C. of each of the vulcanized rubber compositions was measured using a viscoelasticity spectrometer VES manufactured by IWAMOTO Quartz GlassLabo Co., Ltd. under the conditions of an initial strain of 10%, a dynamic strain of 2% and a frequency of 10 Hz.
• the respective test tires were mounted on all wheels of a truck having a maximum authorized freight mass (2-D vehicle). After running a distance of 30,000 km on an unpaved rough road surface where pebbles were scattered, a groove depth of a tire tread portion was measured. Then, a running distance when the tire groove depth was reduced by 1 mm was measured. The result is indicated by an index, and it shows that the larger the index is, the better the abrasion resistance is.
• the index was calculated by the following equation.
• a No. 3 dumbbell type test piece was produced from each of the vulcanized rubber composition according to JIS K6251 and was subjected to tensile test. An elongation at break (EB) was measured, and was indicated by an index, assuming that an index of Comparative Example 1 was 100. The larger the EB index is, the better the chipping resistance of the rubber composition is.
• the tire having a tread composed of the rubber composition for a tread of the present invention comprising a rubber component comprising a predetermined styrene butadiene rubber, isoprene rubber and butadiene rubber is good in abrasion resistance when running on a rough road and has improved overall performances such as abrasion resistance and chipping resistance.
• the tire having a tread composed of the rubber composition for a tread of the present invention is good in abrasion resistance, particularly abrasion resistance for running on a rough road.

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• 2018
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